The invention relates to an apparatus having a directly driven rotating body in accordance with the preamble of claim 1 and to an aerostatic bearing in accordance with the preamble of claim 12.
Such devices are known from WO 02/089671 A2, which discloses an aerostatic rotor bearing for the rotating annular gantry of a computed tomography (CT) scanner. The construction of such CT scanners is generally known, for example, from that document. The disclosure of WO 02/089671 A2 is explicitly referred to herein with respect to the construction of a CT scanner, and its disclosure is incorporated herein by reference.
An imaging apparatus is typically mounted on the annular gantry of a CT scanner, and the imaging apparatus rotates about an area to be examined together with the annular gantry.
In order to clearly image moving bodies, for example a heat beating during examinations with a CT scanner, it is necessary for the rotating gantry to rotate at a sufficiently high speed and to be precisely guided. However, the required high speed can no longer be achieved with systems that are seated on roller bearings due to the required large diameter of the gantry and the resulting high peripheral speed of the bearing bodies. For this reason the device disclosed in WO 02/089671 A2 uses aerostatic bearings.
For aerostatic bearings to function reliably, it is necessary to keep the gap between the opposite bearing surfaces small. Hence, the distance between the opposite bearing surfaces is very small.
Due to the large diameter of the gantry and the asymmetrically mounted imaging equipment, deformations of the annular gantry are encountered, especially at high speeds, so that a predefined size of the bearing gap over the entire rotation of the annular gantry is not guaranteed. Although WO 02/089671 A2 teaches that at least some of the aerostatic bearings are adjustable in order to accurately adjust the air gap, this approach does not allow the deformations of the rotor to be balanced. In particular, when the annular gantry is directly driven, it may lead to alternating magnetic radial forces due to the magnetic forces of the drive that act between the stationary body and the rotating gantry. These magnetic radial forces produce further zonal deformations of the annular rotating gantry and, in addition, induce a dynamic imbalance, which can also be called the “magnetic imbalance”, which cannot be balanced with the adjustable bearings of WO 02/089671 A2.